The principal objective of the proposed research program is to gain a basic knowledge of the fundamental processes of maturation, reproduction and aging in the filarial worms which parasitize man in order that we might understand more clearly and interpret more accurately the clinical manifestations of bancroftian and malayan filariasis. To acheive these goals, the filaria, Brugia malayi, shared by man and primates, and B. tupaiae, a parasite of tupaioids, in natural and experimental hosts, are being utilized as models for laboratory study. Through the long-term study of experimental infections produced with known numbers of worms it will be possible to make a firm assessment of the reproductive potential of the female worm, the relationship worm burden and levels of microfilaremia and the longevity of the adult worms. Also, it is the goal of this research program to clarify the relationships of Dipetalonema streptocerca and the D. perstans-like filariae of primates to their counterparts in man. Efforts will be made to describe in detail, their morphology, distribution and habitats in the definitive host and their role as pathogens using naturally and experimentally-infected monkeys and apes as laboratory models.